EEG asymmetry during aortic arch surgeries associated with selective preferential cerebral hypothermia

Intraoperative EEG monitoring is increasingly used during aortic arch procedures for early detection of acute neurologic dysfunction. In those procedures involving cardiopulmonary bypass, increased neuroprotection may be gained by using hypothermic circulatory arrest and selective cerebral perfusion. Several techniques for cerebral perfusion exist; yet no studies have noted distinct EEG patterns associated with different techniques. In this study, we reviewed EEG records of six aortic arch procedures that used cannulation of the innominate artery to provide selective antegrade cerebral perfusion. In each case, a transient hemispheric asymmetry was noted within 2 minutes of the start of head cooling, consisting of enhanced suppression over the right compared with the left hemisphere, which was confirmed by power analysis. The EEG returned to baseline during passive-head rewarming in five cases, whereas a brief left-sided partial seizure occurred during rewarming in one case. These findings suggest that antegrade cerebral perfusion using cannulation of the innominate artery results in enhanced cooling of the right hemisphere as detected by intraoperative EEG monitoring. Characterization of this finding is necessary to prevent misinterpretation of ischemia by EEG.